1. Field of the Invention
The present invention relates to a fuel supply device supplying highly pressurized fuel to an internal combustion engine, especially a Diesel engine.
2. Description of the Related Art
A conventional fuel supply device has a high pressure pump discharging a highly pressurized fuel, a regulator maintaining the highly pressurized fuel at a constant value, and a fuel injector injecting the highly pressurized fuel maintained at the constant value into an internal combustion engine. The regulator holds the highly pressurized fuel, and has a relief valve to release a part of the fuel to a reservoir when pressure of the fuel exceeds the constant value. Such a fuel supply device construction is described in U.S. patent application Ser. No. 650,719 now U.S. Pat. No. 4,572,136.
It is desirable that the pressure of the fuel supplied to the fuel injector through the regulator be low when the engine is driven at a low speed and light load condition, and high when the engine is driven at a high speed and heavy load condition. In the above conventional device, however, the relief valve operates in such a manner that pressure of the fuel is maintained at a constant value. That is, the pressure of the fuel cannot be freely varied. Further, since the above conventional high pressure pump always discharges a maximum quantity of fuel to be supplied to the fuel injector, the drive force for the pump must have a relatively large capacity.